pack_isam is an extra utility that you get when you order more than 10
licenses or extended support. Since pack_isam is distributed only in
binary form, pack_isam is available only on some platforms.
Of course, all future updates to pack_isam are included in the
price. pack_isam may at some time be included as standard when
we get some kind of turnover for MySQL.
pack_isam works by compressing each column in the table separately.
The information needed to decompress columns is read into memory when the
table is opened. This results in much better performance when accessing
individual records, since you only have to uncompress exactly one record, not
a much larger disk block like when using Stacker on MS-DOS.
Usually, pack_isam packs the data file 40%-70%.
MySQL uses memory mapping (mmap()) on compressed tables and
falls back to normal read/write file usage if mmap() doesn't work.
There are currently two limitations with pack_isam:@:
BLOB columns, yet.
Fixing these limitations is on our TODO list but with low priority.
pack_isam is invoked like this:@:
shell> pack_isam [options] filename ...
Each filename should be the name of an index (`.ISM') file. If you are not in the database directory, you should specify the pathname to the file. It is permissible to omit the `.ISM' extension.
pack_isam supports the following options:@:
-b, --backup
nom_table.OLD.
-#, --debug=debug_options
debug_options string often is
'd:@:t:o,filename'.
-f, --force
pack_isam creates a temporary file named `nom_table.TMD'
while it compresses the table. If you kill pack_isam, the `.TMD'
file may not be deleted. Normally, pack_isam exits with an error if
it finds that `nom_table.TMD' exists. With --force,
pack_isam packs the table anyway.
-?, --help
-j big_nom_table, --join=big_nom_table
big_nom_table. All tables that are to be combined
MUST be identical (same column names and types, same indexes, etc.)
-p #, --packlength=#
pack_isam stores all rows with length pointers of 1, 2 or 3
bytes. In most normal cases, pack_isam can determine the right length
value before it begins packing the file, but it may notice during the packing
process that it could have used a shorter length. In this case,
pack_isam will print a note that the next time you pack the same file,
you could use a shorter record length.)
-s, --silent
-t, --test
-T dir_name, --tmp_dir=dir_name
-v, --verbose
-V, --version
-w, --wait
mysqld server was invoked with the --skip-locking
option, it is not a good idea to invoke pack_isam if the table might
be updated during the packing process.
The sequence of commands shown below illustrates a typical table compression session:@:
shell> ls -l station.* -rw-rw-r-- 1 monty my 994128 Apr 17 19:@:00 station.ISD -rw-rw-r-- 1 monty my 53248 Apr 17 19:@:00 station.ISM -rw-rw-r-- 1 monty my 5767 Apr 17 19:@:00 station.frm shell> isamchk -dvv station ISAM file:@: station Isam-version:@: 2 Creation time:@: 1996-03-13 10:08:58 Recover time:@: 1997-02-02 3:06:43 Data records:@: 1192 Deleted blocks: 0 Datafile:@: Parts: 1192 Deleted data: 0 Datafile pointer (bytes):@: 2 Keyfile pointer (bytes): 2 Max datafile length:@: 54657023 Max keyfile length: 33554431 Recordlength:@: 834 Record format:@: Fixed length table description:@: Key Start Len Index Type Root Blocksize Rec/key 1 2 4 unique unsigned long 1024 1024 1 2 32 30 multip. text 10240 1024 1 Field Start Length Type 1 1 1 2 2 4 3 6 4 4 10 1 5 11 20 6 31 1 7 32 30 8 62 35 9 97 35 10 132 35 11 167 4 12 171 16 13 187 35 14 222 4 15 226 16 16 242 20 17 262 20 18 282 20 19 302 30 20 332 4 21 336 4 22 340 1 23 341 8 24 349 8 25 357 8 26 365 2 27 367 2 28 369 4 29 373 4 30 377 1 31 378 2 32 380 8 33 388 4 34 392 4 35 396 4 36 400 4 37 404 1 38 405 4 39 409 4 40 413 4 41 417 4 42 421 4 43 425 4 44 429 20 45 449 30 46 479 1 47 480 1 48 481 79 49 560 79 50 639 79 51 718 79 52 797 8 53 805 1 54 806 1 55 807 20 56 827 4 57 831 4 shell> pack_isam station.ISM Compressing station.ISM:@: (1192 records) - Calculating statistics normal:@: 20 empty-space: 16 empty-zero: 12 empty-fill: 11 pre-space:@: 0 end-space: 12 table-lookups: 5 zero: 7 Original trees:@: 57 After join: 17 - Compressing file 87.14% shell> ls -l station.* -rw-rw-r-- 1 monty my 127874 Apr 17 19:@:00 station.ISD -rw-rw-r-- 1 monty my 55296 Apr 17 19:@:04 station.ISM -rw-rw-r-- 1 monty my 5767 Apr 17 19:@:00 station.frm shell> isamchk -dvv station ISAM file:@: station Isam-version:@: 2 Creation time:@: 1996-03-13 10:08:58 Recover time:@: 1997-04-17 19:04:26 Data records:@: 1192 Deleted blocks: 0 Datafile:@: Parts: 1192 Deleted data: 0 Datafilepointer (bytes):@: 3 Keyfile pointer (bytes): 1 Max datafile length:@: 16777215 Max keyfile length: 131071 Recordlength:@: 834 Record format:@: Compressed table description:@: Key Start Len Index Type Root Blocksize Rec/key 1 2 4 unique unsigned long 10240 1024 1 2 32 30 multip. text 54272 1024 1 Field Start Length Type Huff tree Bits 1 1 1 constant 1 0 2 2 4 zerofill(1) 2 9 3 6 4 no zeros, zerofill(1) 2 9 4 10 1 3 9 5 11 20 table-lookup 4 0 6 31 1 3 9 7 32 30 no endspace, not_always 5 9 8 62 35 no endspace, not_always, no empty 6 9 9 97 35 no empty 7 9 10 132 35 no endspace, not_always, no empty 6 9 11 167 4 zerofill(1) 2 9 12 171 16 no endspace, not_always, no empty 5 9 13 187 35 no endspace, not_always, no empty 6 9 14 222 4 zerofill(1) 2 9 15 226 16 no endspace, not_always, no empty 5 9 16 242 20 no endspace, not_always 8 9 17 262 20 no endspace, no empty 8 9 18 282 20 no endspace, no empty 5 9 19 302 30 no endspace, no empty 6 9 20 332 4 always zero 2 9 21 336 4 always zero 2 9 22 340 1 3 9 23 341 8 table-lookup 9 0 24 349 8 table-lookup 10 0 25 357 8 always zero 2 9 26 365 2 2 9 27 367 2 no zeros, zerofill(1) 2 9 28 369 4 no zeros, zerofill(1) 2 9 29 373 4 table-lookup 11 0 30 377 1 3 9 31 378 2 no zeros, zerofill(1) 2 9 32 380 8 no zeros 2 9 33 388 4 always zero 2 9 34 392 4 table-lookup 12 0 35 396 4 no zeros, zerofill(1) 13 9 36 400 4 no zeros, zerofill(1) 2 9 37 404 1 2 9 38 405 4 no zeros 2 9 39 409 4 always zero 2 9 40 413 4 no zeros 2 9 41 417 4 always zero 2 9 42 421 4 no zeros 2 9 43 425 4 always zero 2 9 44 429 20 no empty 3 9 45 449 30 no empty 3 9 46 479 1 14 4 47 480 1 14 4 48 481 79 no endspace, no empty 15 9 49 560 79 no empty 2 9 50 639 79 no empty 2 9 51 718 79 no endspace 16 9 52 797 8 no empty 2 9 53 805 1 17 1 54 806 1 3 9 55 807 20 no empty 3 9 56 827 4 no zeros, zerofill(2) 2 9 57 831 4 no zeros, zerofill(1) 2 9
The information printed by pack_isam is described below:@:
normal
empty-space
empty-zero
empty-fill
INTEGER
column may be changed to MEDIUMINT).
pre-space
end-space
table-lookup
ENUM before Huffman compression.
zero
Original trees
After join
After a table has been compressed, isamchk -dvv prints additional
information about each field:@:
Type
constant
no endspace
no endspace, not_always
no endspace, no empty
table-lookup
ENUM.
zerofill(n)
n bytes in the value are always 0 and are not
stored.
no zeros
always zero
Huff tree
Bits